High severity reforming process with a platinum-iridium catalyst

ABSTRACT

NAPTHA FEED STOCKS ARE CONVERTED TO HIGH OCTANE PRODUCTS AT HIGH SEVERITY CONDITIONS UTILIZING A CATALYST COMPRISNG ALUMINA IN ASSOCIATION WITH 0.15 TO 0.75 WEIGHT PERCENT PLATINUM, 0.15 TO 0.45 WEIGHT PERCENT IRIDIUM AND 0.3 TO 2.0 WEIGHT PERCENT CHLORINE, EACH BASED ON TOTAL CATALYST, THE SURFACE AREA OF THE PLATINUM AND IRIDIUM ON THE ALUMINA BEING AT LEAST ABOUT 200 SQUARE METERS PER GRAM OF PLATINUM AND IRIDIUM AS DETERMINED BY CARBON MONOXIDE C CHEMISORPTION TECHNIQUES. THE CATALYST SHOULD CONTAIN LESS THAN ABOUT TWO ATOMS OF SULFUR PER ATOM OF PLATINUM AND IRIDIUM AND BE SUBSTANTIALLY FREE OF ALKALI AND ALKALINE EARTH METAL CONSTITUENTS.

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S EVERITY FACTOR United States Patent O M US. Cl. 208-139 8 Claims ABSTRACT OF THE DISCLOSURE Naptha feed stocks are converted to high octane products at high severity conditions utilizing a catalyst comprising alumina in association with 0.15 to 0.75 weight percent platinum, 0.15 to 0.45 weight percent iridium and 0.3 to 2.0 weight percent chlorine, each based on total catalyst, the surface area of the platinum and iridium on the alumina being at least about 200 square meters per gram of platinum and iridium as determined by carbon monoxide chemisorption techniques. The catalyst should contain less than about two atoms of sulfur per atom of platinum and iridium and be substantially free of alkali and alkaline earth metal constituents.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of Ser. No. 194,461, filed November 1, 1971 which, in turn, is a continuation-in-part of Ser. No. 883,601, filed Dec. 9, 1969, now abandoned.

BACKGROUND OF THE INVENTION A Field of the Invention This invent'ion relates to a high severity naphtha reforming process utilizing a supported platinum/iridium catalyst. More. particularly, the present invention relates to the use of an alumina supported platinum/iridium/ chlorine catalyst in a naphtha hydroforming operation conducted at high weight hourly space velocity conditions.

Description of the Prior Art The use of iridium-containing catalysts. in naphtha reforming operations has been reported in the patent literature. Webb et al., US. 2,848,377, disclose that supported iridium/platinum metal combinations are effective hydrocarbon conversion catalysts. Sinfelt et al., in US. 3,567,625, teach that combinations of iridium with Group IB metals are effective hydroforming catalysts. Koberstein, in German Pat. 1,108,361, teaches that supported platinum catalyst containing minor amounts of iridium can be employed to reform heavy petroleum fractions. Further, the patentees of US. 3,487,009; US. 3,507,780; US. 3,507,781; US. 3,554,902 and US. 3,578,583 disclose the existence of various types of supported iridium-containing catalysts and their use in the hydroforming of naphtha fractions.

SUMMARY OF THE INVENTION 'the course of the reforming operation. In particular, it

has been discovered that alumina supported platinum/ Patented Sept. 10, 1974 iridium/chlorine catalysts can be successfully employed in naphtha hydroforming operations at space velocity conditions beyond those obtainable with commercially available reforming catalysts at identical process con ditions.

BRIEF DESCRIPTION OF THE DRAWING The figure illustrates the relationship between severity factor (as hereinafter defined) and the weight hourly space velocity obtainable in a semi-regenerative reforming operation wherein platinum/iridium catalysts and commercially available platinum/rhenium and platinum catalysts are used to reform a naphtha feed stock having a Watson characterization factor of from 11.4 to 12.2 at a temperature ranging from about 750 to 1050 F. and a pressure varying from about to 600 p.s.i.g. In general, the lower operating line of each band represents the performance level obtainable with a difiicultly reformable feed and the upper operating line represents the performance level obtainable with an easily reformable feed.

.fjThe reforming of petroleum naphthas to products having increased octane numbers utilizing noble metal type catalysts is a well-known refinery process. Basically, there are two types of reforming units, namely, semiregenerative type units wherein the unit is on-stream for two or more months between catalyst regenerations and cyclic units wherein the catalyst is regenerated morefrequently. The present invention is concerned with a reforming process carried out in the semi-regenerative mode. In a typical semi-regenerative process, the catalyst is maintained as a fixed bed within a number of serially connected, adiabatically operated reactors. The naphtha feed stock, preferably a substantially sulfur-free naphtha feed stock, is mixed with hydrogen, generally contained in a recycle gas, and heated in a pre-heat furnace and/ or by indirect heat exchange with a products tream and in troduced to the first reactor of thereactor train. The efiluent from the first reactor is passed'through a reheat furnace and introduced to the second reactor in the train. This sequence is repeated as the process efiiuent is treated in subsequent reactors. The temperature to which the feed and hydrogen are heated depends on the condition of the catalyst within individual reaction zone. With a fresh or freshly regenerated catalyst, the inlet temperatures to each reaction zone may be as low as 875 F. During' the course of the reforming reaction, carbonaceous residues deposit on the catalyst and the catalyst activity diminishes. This deactivation requires that the feed stock and hydrogen be heated to a higher inlet temperature to maintain the same product octane level. Thus, reaction.

temperature is normally slowly increased during the onstream period to maintain constant octane. The maximum reactor inlet temperature, generally about 1000- 1050" F., is set by the onset of rapid catalyst deactivation.

After the reactants pass through the reactors and the re-- the. period between catalyst regenerations or the period between start-up with fresh catalyst and the first regen-- eration, or maximum throughput (space velocity) to obtain. a product having a given octane level. Ordinarily,

when operating at maximum space velocity, high severity process conditions need to be employed and the catalyst deactivates rapidly due to the increased rate of deposition of carbonaceous residues on the catalyst. As a result, the unit must be taken oif stream and the catalyst regenerated. According to the present invention, it has been discovered that a very specific type of supported platinum/iridium catalyst can be employed in a semi-regenerative naphtha reforming process at severity conditions beyond the capability of commercially available platinum and platinum/ rhenium catalysts with prolonged on-stream periods and without substantial incycle yield losses, This unusual performance capability is illustrated in the figure. In the figure are presented operating bands A, B and C. These bands encompass the range of practical operations which might be employed with each catalyst based upon correlated laboratory, pilot plant, literature, and refinery data. As is evident from the figure, at any given severity factor the specific platinum/iridium catalyst of the present invention (band A) can be employed in a semi-regenerative reforming operation at space velocities considerably higher than those possible with a platinum/rhenium catalyst (band B) or a conventional platinum catalyst (band C).

The catalyst employed in the semi-regenerative reforming process of the present invention comprises alumina, preferably eta or gamma alumina or mixtures thereof, in association with 0.15 to 0.75 Wt. percent platinum, 0.15 to 0.45 wt. percent iridium, and 0.3 to 2.0 wt. percent chlorine promoter, each based on the total weight of anhydrous catalyst. Of course, other constituents may be present on the catalyst. The surface area of the plantinum and iridium present on the alumina must be maintained at a level of at least about 200 square meters per gram (mF/ gm.) of platinum and iridium present, as determined by carbon monoxide chemisorption techniques (see Sinfelt and Yates, J. Catalysis, 8, 82-90 (1967)). The catalyst should contain less than about two atoms of sulfur per atom of platinum/iridium present in the catalyst and further be substantially free of alkali or alkaline earth metal constituents,

The platinum/iridium catalyst can be prepared by impregnating the alumina support material with a solution of a soluble iridium compound and a soluble platinum compound. Desirably, an aqueous solution of the metal compounds is used. It is essential that the metal compounds be impregnated on the alumina simultaneously to maximize the desired interaction between the iridium and platinum and thus promote the formation of a highly dispersed cluster structure in the final reduced form of the catalyst. The alumina is impregnated with an aqueous solution of decomposable compounds of iridium and platinum in sufficient concentration to provide the desired quantity of metal in the finished catalyst. Iridium and platinum compounds suitable for incorporation onto the alumina support material include, among others, chloroiridic acid, iridium tribromide, ammonium chloroiridate, iridium trichloride, chloroplatinic acid, ammonium chloroplatinate, platinum amine salts, etc.

Followng the impregnation of the alumina with the iridium and platinum compounds, the composite catalyst is dried at a temperature varying from about 220 to 250 F. The catalyst may be dried in air at the abovestated temperatures or may be dried by treating the catalyst in a flowing stream of hydrogen or inert gas. The drying step may be followed by an additional calcination at a temperature of about 500-700 F. Care must be taken to avoid contacting the catalyst at temperatures in excess of about 800 F. with an oxygen-containing gas. Otherwise the iridium will be oxidized, with loss of surface area, to crystallites of iridium oxide, and the polymetallic cluster structure will not be obtained on reduction.

A halogen, particularly chlorine, is a necessary catalyst constituent and is normally present in amounts varying from ab ut 0.3 to 2.0 wt. percent, preferably 0.6 to

1.5 wt. percent, based on total dry weight of the catalyst. The halogen may be incorporated into the total catalyst composite at any stage in the catalyst manufacture, i.e., before, during or after incorporation of the catalyst metals onto the alumina. Halogen is often incorporated into the catalyst when impregnating the support with halogen bearing catalyst components such as chloroiridic acid and chloroplatinic acid. Further amounts of halogen may be incorporated in the catalyst by contacting it with chlorine, hydrogen chloride, ammonium chloride, C C 'alkyl chlorides, etc., either during catalyst preparation or in subsequent use.

As stated previously, the specific platinum/iridium catalyst is capable of reforming a naphtha feed stock to a high octane product at unusually high weight hourly space velocity conditions. More specifically, the instant catalyst system can be used in a naphtha reforming process wherein hydrogen and a naphtha feed stock having a Watson characterization factor of from about 11.4 to 12.2 are contacted in the presence of the catalyst at a temperature of less than about 1050 F., preferably from about 750 to 1000 F., a pressure of from about 150-600 p.s.i.g., and a hydrogen to naphtha feed stock molar ratio (H/O) of from about 2.5 :1 to 8:1 to produce a C reformate product having a research octane number (RON), as determined by ASTM test D-2699-68, of from about 94 to 102 for an on-steam period (X) of from 3 to 24 months without incurring a C9 liquid yield decline of greater than about 3.0 volume percent during said on-steam period, as determined from a base yield obtained 200 hours after the initial contacting of the naphtha feed stock and hydrogen with fresh or freshly regenerated catalyst. The process is characterized by carrying out the contacting operation at a weight hourly space velocity (pounds of feed per hour per pound of catalyst) beyond the limits normally possible with a conventional catalyst, specifically within the limits of band A of the figure. Severity factor equals 21.8'9+0.22 (RON) 0.35 In (H/'O)+0.50 ln (X), and applies to RON variations from 94 to 102, H/O variations from 2.5 :1 to 8:1 and X variations from 3 to 24 months. In a preferred system, the process is carried out at pressures varying from 150 to 400 p.s.i.g. with a catalyst comprising 0.3 Wt. percent platinum, 0.3 Wt. percent iridium, and 0.6-1.5 wt. percent chlorine on alumina, the amounts of catalyst components present being based on the total anhydrous weight of the catalyst.

In general, the high space velocity levels can be achieved when processing a wide variety of naphtha feed stocks with the catalyst of the present invention. Suitable feeds include substantially sulfur-free naphtha streams that typically contain about 15-80 volume percent paraffins, 15-80 volume percent naphthenes, and about 2-20 volume percent aromatics and that boil at atmospheric pressure at temperatures substantially between about and 450 F., preferably between about and 375 F. In general, any naphtha feed stock having a Watson characterization factor '(K,,) of from about 11.4 to 12.2 can be processed to high octane C liquid products using the process of the present invention. The Watson characterization faotor is a well-known index of the chemical character of petroleum fractions. Materials having a high Watson characterization factor are more difiicult to convert to high octane products than naphtha feeds that have lower Watson characterization factors. The Watson characterization factor of a petroleum fraction is equal to the cube root of the mean average boiling point in degrees Rankine divided by the specific gravity at 60 F. Mean average boiling point is defined as the boiling point of the petroleum fraction which best correlates the molecular weight of the fraction. The mean average boiling point of a petroleum fraction can be determined by means known to those skilled in the art and is typically obtained, using known correlations, from the volume average boiling point of the petroleum fraction which in turn is obtained by integrating or averaging the distillation curve of said fraction (temperature versus liquid volume percent distilled). Further information regarding the determination of mean average boiling point of petroleum fractions can be obtained by reference to Data Book on Hydrocarbons, B. Maxwell, D. Van Nostrand Company, Inc., 1950.

As is evident from the figure, the space velocity that may be used in an operation to produce high octane C reformate with minimal yield loss is much greater for platinum/iridium catalyst than for platinum or platinum/ 'rhenium. This result is true for either a poor quality feed, such as a highly paraffinic material, or an easily reformed feed, such as a medium boiling naphthenic material. The fact that higher space velocities can be used is commercially significant since the refiner can use much less catalyst or secure a much higher throughput than would normally be possible.

What is claimed is:

1. A naphtha reforming process comprising contacting a naphtha feed stock having a Watson characterization factor of from about 11.4 to 12.2 and hydrogen with a catalyst comprising alumina in association with 0.15-0.75 wt. percent platinum, 0.15-0.45 wt. percent iridium and 0.3-2.0 wt. percent chlorine, each based on total anhydrous catalyst, the surface area of said platinum and iridium on said alumina being at least about 200 square meters per gram of platinum and iridium, as determined by carbon monoxide chemisorpti-on techniques, said catalyst containing less than about two atoms of sulfur per atom of platinum and iridium and being substantially free of alkali and alkaline earth metal constituents, said contacting being conducted at a temperature of less than about 1050 F. and a pressure of from about 150 to 600 p.s.i.g. at a hydrogen to naphtha feed stock molar ratio (H/O) of from about 2.5:1 to 8:1, to produce a C reformate product having a research octane number clear (RON) of from 94-102 for an on-stream period (X) of from 3 to 24 months without incurring during said onstream period a C liquid yield decline greater than 3.0

conducted at a pressure varying from about to 400 p.s.i.g.

4. The process of claim 1 wherein said contacting is conducted at a temperature in the range of from about 750 to 1000 F.

5. The process of claim 1 wherein said catalyst contains from 0.6 to 1.5 wt. percent chlorine.

6. The process of claim 1 wherein said catalyst contains about 0.3 wt. percent platinum, 0.3 wt. percent iridium and about 0.6 to 1.5 wt. percent chlorine.

7. The process of claim 6 wherein said contacting is conducted at a pressure varying from about 150 to 400 p.s.i.g.

8. The process of claim 7 wherein said cont-acting is conducted at a temperature in the range of from about 750 to 1000 F.

References Cited UNITED STATES PATENTS 2,848,377 8/1958 Webb 208-138 2,911,357 11/1959 Myers et a1. 208-438 DELBER'I' E. GANTZ, Primary Examiner S. L. BERGER, Assistant Examiner US. Cl. X.-R. 252-441 

